The present invention relates to the field of liquid measuring, in general, and more particular, to the measurement of a height and/or quantity of the liquid in a container based on area image processing of one or more light patterns projected onto the liquid surface.
Sensing a distance to an object using a projected beam of light is well known. For example, U.S. Pat. No. 5,521,694 (the xe2x80x9c""694 patentxe2x80x9d) is directed to a system utilizing a laser beam for sensing distance to an object for identifying characteristics of a liquid in a container, like the level of the liquid, the identification and locations of interfaces between liquids and identifying particles in a liquid at different depths and locations among other physical features of the liquid. The system of the ""694 patent generates a laser beam to an object, like the surface of a liquid, for example, and receives light reflected from the surface through an optical arrangement that projects a spot image onto a linear array of photo diodes or charge coupled devices (CCDs). The resulting output of the linear array is processed to determine the distance to the object surface. Individual elements of the array are electrically separated from each other to create a built in micro scale for use as fixed reference points in identifying distance to the object. These types of systems rely solely on a single point of light are thus highly sensitive to alignment of its optical elements which may easily be disturbed by external forces such as vibrations, shocks and the like. Accordingly, any disturbance in alignment will cause significant errors in measurement.
Another application for sensing distance to an object with projected light is in conventional auto focus cameras. For example, the U.S. Pat. Nos. 5,274,429 and 5,253,032 are directed to distance measuring systems using one or more projected light beams to determine the focal distance to a desired object to be photographed. These systems propose to solve the problem of autofocusing when there is more than one object to be photographed in a common frame of the camera. The ""429 patent is directed to projecting light beams to a plurality of distance measuring points and receiving the reflected light beams from said points onto photo sensing devices (PSDs). While the patent describes various embodiments using a plurality of light sources and plurality of PSDs, all of the embodiments appear to process only the photocurrents output from the PSDs and the ratios thereof for focal distance determination. The ""032 patent is directed to the use of modulated infrared (IR) light and a PSD which outputs photocurrents in accordance with the incidence position of the reflected light from the desired object or objects to be photographed. These types of systems are not of the variety that measure a physical quantity of the object from the resulting distance measuring data.
The present invention proposes to solve the drawbacks of these background systems by simplifying the structure and relying more on the processing of area image patterns for the determination of object distances to measure physical quantities of a liquid, thus diminishing the sensitivity to alignment of optical elements and improving the accuracy of the liquid measurements.
In accordance with the present invention, Apparatus for measuring height of a surface of liquid in a container comprises a light source disposed above the liquid surface for illuminating the liquid surface with a pattern of light; means for capturing an area image of the light pattern in a form of discrete picture elements (pixels); and means for processing the pixels of the area image to determine the height of said liquid surface in the container. In one embodiment, the processing means includes means for processing the pixels of the area image to determine attitude of the liquid surface in the container; a memory for storing data representative of the geometry of the container; and means for determining the quantity of liquid in the container based on the determined height and attitude of the liquid and the container geometry data.
In accordance with another aspect of the present invention, the apparatus for measuring height of a surface of liquid in a container comprises a plurality of light sources disposed above the liquid surface, each light source for illuminating a portion of the liquid surface with a pattern of light; image capturing means corresponding to each light source of said plurality, each means for capturing an area image of said light pattern illuminated by its corresponding light source in a form of discrete picture elements (pixels); and means for processing the pixels of the area image of each image capturing means of said plurality to determine the height of said liquid surface in the container. In another embodiment, each light source and its corresponding image capturing device are disposed in a predetermined spatial relationship with each other to function together as a pair for a predetermined portion of the liquid surface; and the processing means processes the pixels of the area image of each image capturing means to determine the heights of the liquid surface for the corresponding predetermined portions.
In accordance with a further aspect of the present invention, the apparatus for measuring height of a surface of liquid in a container comprises at least one light source disposed above the liquid surface for illuminating the liquid surface with at least one pattern of light; a plurality of image capturing means disposed above the liquid surface for observing the at least one light pattern at different viewing angles, each means for capturing an area image of said at least one light pattern in a form of discrete picture elements (pixels); and means for processing the pixels of the area image of each image capturing means to determine at least one height for the liquid surface in the container. In yet another embodiment, the processing means includes means for combining together the pixels of the area images of the plurality of image capturing means to determine the at least one liquid surface height.